This invention relates to a gear transmission apparatus for use in a vehicle or the like.
An engine accessory drive apparatus is disclosed in Japanese Patent Publication No. 24605/1983. In this apparatus, an internal gear is coupled to a casing through an electromagnetic clutch to put a planetary gear mechanism into a speed-change state.
With the above-mentioned structure including the electromagnetic clutch, an electromagnet and a clutch portion must be located between the planetary gear mechanism and the casing. Accordingly, the apparatus inevitably has a large size in an axial direction. The internal gear located at the side of a brake is cantilevered and has a free end. Since no centering function of the free end is provided, the internal gear often becomes eccentric when subjected to an external Force from the electromagnetic clutch. In this event, normal engagement can not be maintained between the internal gear and other gears. This results in vibration, noise, deterioration of durability, and damage of the gears.
Japanese Utility Model Laid Open No. 173854/1983 discloses an engine accessory drive apparatus with a planetary gear mechanism. The disclosure is directed to a gear transmission mechanism. The planetary gear mechanism includes an internal gear, a pinion carrier, and a sun gear. One of the internal gear, a pinion carrier, and a sun gear is braked by a braking unit to provide a speed-change state.
The braking unit comprises a vacuum actuator. A vacuum may be derived from a vacuum pump or a suction side in an engine drive section. In any event, an output characteristic of an engine is unfavorably affected if the vacuum actuator is used. Alternatively, a hydraulic actuator may be used instead of the vacuum actuator. In this case, when an oil pump for lubrication of the engine is used in common for the hydraulic actuator, a risk of oil leakage increases because a hose is extended around to supply hydraulic fluid. The oil leakage often results in lubrication failure of the engine. On the other hand, installation of an additional oil pump is not desirable in view of an arrangement space. Thus, the above-mentioned structure with a pressure source is disadvantageous because the output characteristic of the engine is unfavorably affected. In addition, it is difficult to optionally incorporate such a structure as a post-fixial assembly because a wide range of modification is necessary including extension of a pressure supply pipe.